1. Field of the Invention
The present invention relates generally to multiple processor computer systems and more specifically to the assignment of resources to computer system processes. More particularly, the present invention relates to the dynamic assignment of input/output resources to application programs in an asymmetric multiple processor computer system in which input/output resources exist on a subset of the multiple processors.
2. Background and Related Art
Multiple processor computer systems are those in which more than one processing element or CPU is used to process a given workload. A multiple processor system may have two, four, or more processors within a computer cabinet or in several enclosures connected to form a single processing entity.
Symmetric multiprocessors (SMP) have shared memory that is accessible by all of the processors in the complex. Shared memory enables the task scheduling function of the system to assign a task to the processor that has the necessary resources for that task. Such resources may include input/output devices such as displays, printers, or communications devices. In a symmetric multiprocessing system the shared memory environment enables a task to be scheduled on a processor with a certain resource and later rescheduled through the shared memory to a different processor.
Asymmetric multiple processor systems contain resources that are physically attached to only a subset of the processors. An asymmetric system includes configurations such as clustered computer systems which may reside in different processor cabinets and be linked by a high speed bus or switching mechanism. The scheduler in prior art asymmetric multiple processor systems typically assigns an application to a processor having the resources required to complete the application execution. The application is statically bound to the processor with the resources. There is no provision for unbinding the application from a processor and there is no ability to reschedule the application process on a different processor with different resources during its execution.
An asymmetric multiple processor system according to the present invention is shown generally in FIG. 1 as 100. Computer processors C1-C3 102, 104, 106 each have certain resources attached R1-R7. Resource 1 108 is physically attached to processor C1 102. Only processor C1 can directly access or use resource 1 108. Indirect access to the resource is provided by, for example, sending an interprocess message to the processor with the required resource. Indirect access is costly to performance and much less desirable than direct access. The number of resources assigned to any one processor depends upon the particular system structure. A cluster of computer systems may have all resource attached to a single processor or they may be distributed evenly among the processors. The specific allocation of resources to processors is immaterial to the present invention.
Resources such as permament storage disk devices 120 can be shared among processors. The sharing of disk resources enables the processors to communicate and to cooperate in the execution of applications. The ability to be shared amongst processors depends on the type of resource. Typically, the input/output resources other than disk devices can only be attached to a single processor and cannot be shared between or among processors.
Prior art asymmetric multiprocessing systems have a technical problem in that static binding of applications to processors creates load balancing and performance problems. If several applications require access to a particular resource, e.g. R1 108, the processor C1 supporting that resource can become overloaded while the other processors in the complex lack work. This results in poorer system throughput due to the bottleneck of C1. A second problem arises when an application requires access to different resources on different processors. If a particular application requires the use of R1 108 and R3 110, a scheduling problem results. The prior art systems also do not effectively handle the case where less than all of the processors have access to a particular resource. If, for example, only two of the three processors were able to access a device, prior art asymmetric multiprocessing scheduling would enable only one processor to be statically bound to an application process and would not perform any load balancing between the subset of processors.
A technical problem therefore exists to develop a method and system to enable dynamic scheduling of applications and processes using resources that are shared by one or more, but less than all of the processors in an asymmetric multiple processor complex.